138 research outputs found
KNO scaling of fluctuations in pp and pA, and eccentricities in heavy-ion collisions
Multiplicity fluctuations at midrapidity in p+p collisions at high energies
are described by a negative binomial distribution and exhibit approximate
Koba-Nielsen-Olesen (KNO) scaling. We find that these KNO fluctuations are
important also for reproducing the multiplicity distribution in d+Au collisions
observed at RHIC, adding to the Glauber fluctuations of the number of binary
collisions or participants. We predict that the multiplicity distribution in
p+Pb collisions at the LHC also deviates little from the KNO scaling function.
Finally, we analyze various moments of the eccentricity of the particle
production zone in A+A collisions at RHIC and LHC and find that particle
production fluctuations increase fluctuation dominated moments such as the
triangularity epsilon_3 substantially.Comment: 7 pages, 6 figures; v2: updated references and a few minor
modifications, to appear in PR
Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions
Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good--Walker formalism the cross section is determined by the fluctuations in
the interaction. In this paper we show that by taking the fluctuations in the
BFKL ladder into account, it is possible to describe both low and high mass
excitation by the Good--Walker mechanism. In high energy collisions the
fluctuations are strongly suppressed by saturation, which implies that pomeron
exchange does not factorise between DIS and collisions. The Dipole Cascade
Model reproduces the expected triple-Regge form for the bare pomeron, and the
triple-pomeron coupling is estimated.Comment: 20 pages, 12 figure
Lattice calculation of hybrid mesons with improved Kogut-Susskind fermions
We report on a lattice determination of the mass of the exotic
hybrid meson using an improved Kogut-Susskind action. Results from both
quenched and dynamical quark simulations are presented. We also compare with
earlier results using Wilson quarks at heavier quark masses. The results on
lattices with three flavors of dynamical quarks show effects of sea quarks on
the hybrid propagators which probably result from coupling to two meson states.
We extrapolate the quenched results to the physical light quark mass to allow
comparison with experimental candidates for the hybrid meson. The
lattice result remains somewhat heavier than the experimental result, although
it may be consistent with the .Comment: 24 pages, 12 figures. Replaced to match published versio
Extracting the Distribution Amplitudes of the rho meson from the Color Glass Condensate
We extract the leading twist-2 and subleading twist-3 Distribution Amplitudes
(DAs) of the rho meson using the HERA data on diffractive rho photoproduction.
We do so using several Colour Glass Condensate (CGC) inspired and a Regge
inspired dipole models. We find that our extracted twist-2 DA is not much model
dependent and is consistent with QCD Sum Rules and lattice predictions. The
extracted twist-3 DA is more model dependent but is still consistent with the
Sum Rules prediction.Comment: 21 pages, 10 figures, 3 tables. Section 6 revised, figures 8 and 9
and table 3 updated. Conclusions essentially unchange
Elastic and quasi-elastic and scattering in the Dipole Model
We have in earlier papers presented an extension of Mueller's dipole cascade
model, which includes sub-leading effects from energy conservation and running
coupling as well as colour suppressed saturation effects from pomeron loops via
a ``dipole swing''. The model was applied to describe the total and diffractive
cross sections in and collisions, and also the elastic cross
section in scattering.
In this paper we extend the model to describe the corresponding quasi-elastic
cross sections in , namely the exclusive production of vector mesons
and deeply virtual compton scattering. Also for these reactions we find a good
agrement with measured cross sections. In addition we obtain a reasonable
description of the -dependence of the elastic and quasi-elastic
cross sections
Probing collective effects in hadronisation with the extremes of the underlying event
We define a new set of observables to probe the structure of the underlying
event in hadron collisions. We use the conventional definition of the
`transverse region' in jet events and, for a fixed window in jet ,
propose to measure several discriminating quantities as a function of the level
of activity in the transverse region. The measurement of these observables in
LHC data would reveal whether, e.g., the properties of `low-UE' events are
compatible with equivalent measurements in collisions (jet
universality), and whether the scaling behaviour towards `high-UE' events
exhibits properties of non-trivial soft-QCD dynamics, such as colour
re-connections or other collective phenomena. We illustrate at
TeV that significant discriminatory power is obtained in comparisons between MC
models with varying treatments of collective effects, including Pythia 8, EPOS,
and Dipsy.Comment: 23 pages, 8 figure
- …